Radio signaling system



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INVENTOR d MTDRNEY Feb. 11, 1930. M EsPENscl-UED RADIO SIGNALING SYSTEM Original Filed Jan', 17, 192,3

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,46 imost any Patented Feb. 1,1, 1930 UNITED STATES PATENT OFFICE \LLOYD ESPENSCHIED, OF HOLLIS, NEW YORK, ASSIGNOIl, TO AMERICgAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK RADIO SIGNALING SYSTEM Original application led January 17, 1923, Serial No. 613,226, which, in.turn, is a division o! my Patent No. 1,446,890, dated February 27, 1923. Again divided and this application led December 10, 1924.

Serial No. 755,076.

AThis invention relates generally' to systems fortransmitting energy and particularly t the protection of such systems against disturbance. Its object is to provide a method.

of and ap aratus for eliminating or minimizing the e ects of disturbances in such systems,

Whether in power circuits or signaling systems, and in either wire or wireless systems of communication. The invention finds one very important application in the radio transmission of intelligence as a protection against the electrical disturbances commonly known i as` static; and the invention will be here described as applied to such a system, but, as will clearly appearphereinafter, the invention is of much broader applic-ability.

This application is a division of my coending application. Serial No. 613,226, filed anuary 17, 1923, which in turn, is a division of an application of mine which issued on February 27, 1923 as Patent No.- 1,446,890.

In radio signaling systems the usual antenna is sharply tuned to increase its responsiveness to waves of the particular frequency to be '25 received and to reduce the liability of interference, from signals of other frequencies. The effect of static disturbances upon an antenna thus sharply tuned seems to be analoous to that of a blow upon a tuning fork, that 1s the energy of the impact is converted largel into oscillations of the frequency to which the device is tuned. In a wireless receiving system this means that the disturbance will appear in the receiver to the confusion of the signals it is desired to observe. In other words the receiving systems, instead of excluding the static disturbances by reasonV ofV existing differences between them and the signaling impulses, or instead of accentuattends to eifectually extinguish the differences that do exist, so that the disturbance is in a sense manufactured by the system for its own" receiver., Like phenomena may occur in a1- some or ally of the transmitting medium has a natural period or is capable of responding syrnlnfpathetcally to foreign disturbances.

isl inventionfproposes to -avoid suchv disturbance by changing or diverting thedisor 'producing differences between them,

energy transmission 'system where The invention will be more fully' understood by reference tothe following description and the accompanying drawing in which Figure 1 is a diagrammatic illustration of the receiving end of a radio signaling system y embodying theinvention and in which a wave filter form of antenna is em loyed.

Fig. 2 is a variant of t e arrangement shown in'Fig. 1.

Fig. 3 is a curve lndicatinggenerally the operation of the system.

In Fig. 1,1() represents the antenna of the receiving circuit arranged in the form of wave filter, consisting of a horizontal conductor 11 grounded at intervalskas shown, by

vertical conductors 12. Impedance, here shown as capacities 13 and inductances 14, is located in each section of the horizontal conductor, that is, between each two grounded conductors.l Eachv grounded conductor. is also provided with impedance, vshown in this instance .as a capacit 15 and an inductance 1 6, arranged in paral el.

The wave filter perse 1s the invention of G.-

A. Campbell, and, as disclosed in his Patentl 1,227,113, May 22, 1917, may assume any one of several forms. Thus, for the purposes of tuning to respond to different frequencies,

any Vset of inductances or capacities above indicated, may be omitted, or their values adjusted.

Af-.circ'uit of this character has a plurality of natural frequencies ,andv at the same time is capable of responding to Vforced or sustained 4alternatinr f current excitation overa considerable range orband of frequencies.'

v17 re resents the usual tuned receivin circuit, w ich is in ,this case tuned sharp yv to the frequency of the signal to be received. Between this and the antenna is placedv a device 18 for the purpose of preventing reaction, between lthe sharply tuned circuit'. 17

tuned and coupled with the and the filter circuit. In the present instance, this is illustrated as an audion having the usual filament, grid and plate. and the batteries A, B and C for controllingvits action. When the audion is used for this purposeg it is adjusted to amplify to a large degree in transmitting energy from the filter circuit to the tuned circuit 17, in which case its effect when transmitting in the opposite direction is negligible. This prevents the circuit 17 from-becoming in effect one section of the antenna circuit and partaking in forming the natural oscillations of various frequencies present in that circuit. The device 18 may conveniently be called a one-Way device by reason of the characteristic 'ust pointed out. It is possible to omit it entirely if the coupling between the tuned circuit 17 4and the antenna is made sufficiently loose to prevent the undesired reaction mentioned.

The device 18 is connected to the antenna circuit by conductors 19, which ,are here shown as terminating at the end vertical conductor, though it willbe understood that this connection may be otherwise located. Transformers 20 and 21 are interposed, as usual, in the circuit at either side of the one-way device to localize the battery currents hnd to give any desired ratio of transformation.

22 is a detector for the signaling current,

here shownas of the audion type and operating in a well known manner. 'It is coupled with the receiver 23 by transformer 24 in the usual way.`

In Fig. 2 a different form of antenna is illustrated. It is composed of a conductor having a vertical component 30 and a horizontal component 31 in each of which are located inductances and capacities 32 and 33 in much the same manner as in the horizontal conductor the modification shown in Fig. 1. As is well known, an antenna, especially one with a horizontal component, as illustrated in this figure, has a natural ca acit to round which may be regarded as istribute along the antenna somethin after the fashion of the ca acities 15 in ig. 1. The antenna here s own will, therefore, when properly other elements of the receiving circuit above described, operate as a Wave filter having a plurality of natural frequencies. Here, the one-way device, the tuned circuit, the detector and the receiver, `correspond to those described in con- `nection with Fig. 1.

Fig. 3 is a curve illustrating theI o ration of the receiving circuit, in which t e ordinates represent current and the absciss frequenc The line c: indicates the band of frequencies to which the filter circuit will respond for sustained or forced alternating current. Lines y indicate the naturatfrequenc `eriods to which the filter circuit is ad]uste our such 'frequencies are indicated in this instance corresponding to the four natural periods of the four section filter circuit shown. In general, for the simple form of antenna in Fig. 2, .the number of natural periods corresponds to the number of sections of the filter circuit. For the more general form of filter circuit in which both the series and the shunt-branches contain both inductance and capacity, as in Fig. 1, each section exhibits two degrees of freedom, the number of natural periods being then twice the number of sections. The curve a indicates the resonance characteristic of the sharply tuned circuit 17. The frequencies to which this circuit will respond are located, it will beobserved, in a very narrow band between the natural frequencies of the filter circuit. It will be understood that this circuit mi ht be tuned to a frequency lying beyon the natural frequencies of the filter circuit in either direction if the responsiveness of the filter to forced alternating current im ulses were made sufficiently broad to allow o such an adjustment.

The operation 'of the receiving circuit will now be `readily understood. Static disturbances falling upon the filter circuit are largely converted into oscillations of a plurality of definite frequencies, or bands of frequencies of limited extent, which corresponds to the natural frequencies of the circuit. These oscillations, being relatively persistent and for the most art at least, different from the signaling re uency, are discriminated against by the sharp y selective circuit 17. The signaling impulses are of a frequency differing from the natural frequencies of the circuit and are received through the filter circuit by reason of its responslveness to forced alternating current impulses, as indicated by the curve :v in Fig. 3. Thesepass through the one-way device 18 which, in this case, also amplifes them, into\ the tuned circuit 17 to the detector22, andy thus to the receiver, in the usual manner. Inasmuch as the static disturbance is for the/ most part dissipated into frequencies other than the signahng frequency, no a preciable interference with the signals wil result.

If the filter circuit is adjusted so that the natural fr uencies thereof are each r resented by a and of more or less extent, 1t is possible that these may, in some cases, la over the signaling frequency. If the ban s were concelved as extending toward each4 other-until they merge this would be true in all cases, but even under these conditions the energy of the static disturbance is spread out, so to speak, over a large number of frequencies, while the signaling frequency is sharply limited, and the resultlng disturbance/ in the receiver would be proportionately reduced.

Since this method of differentiation is based upon the difference which exists between the disturbance and the signaling cur motors,

rent as regards persistency, it is obviously desirable that this difference be preserved to the point at which the currents enter the frequency-concentrating filter. This desirable condition is fulfilled in the or anization of Fig. l, by incorporating the fi ter action in the antenna itself so that immediately upon the transference of the energy of the free electric Waves into current orm, the filter actionbecomes effective. This is likewise the case in the system of Fig. 2.

It will now be evident that the broad method herein employed for differentiating between impulsesand steady state forces, or between oscillations of different degrees of persistency, is a general method and is not limited to the application herein described in detail, but is applicable irrespective of the ty e of transmission system (i. e. Whether using natural media or wires) or of the forni of the energy involved, Whether electrical or mechanical, or of the absolute values of the frequencies concerned. In the sphere of Wireless transmission, for instance, the method is not limited to electric wave transmission Which is usually conducted at ultra-audible frequencies, but may be invoked as well in audible sound-Wave transmission, as in submarine signaling.

In this latter art l compression and rarefactioiid aregenerated by forces applied mechanically tothe water. In the case of ordinary submarine signaling, continuously generated sound waves producing in the receiver a musical note are usually employed; and these Waves are generated at the transmitter by the rythmic motion of 'a diaphragm in the water; Detection of vessels by underwater sound transmission may be accomplished by reason of the waves which are set up in the water by thepropelling machinery of the vessel, the driving engines or or the propellers themselves. The receiving of such submarine signals as these is, however, frequently interfered with by the presence in the Water of extraneous pressure Waves, caused by surface waves, etc., which act upon the receiving diaphragm and attendant receiving circuits in much the .same Way as ds static upon a radio' receiving system, and this lmay be eliminated by the invention here described.

It Will be understood that the method de scribed may also be used in the art of wire electric transmission systems of all lrinde. While free transmission systems such as radin and submarine signaling systems are peculf efe not entirely free from this dimculty..

iarly subject to the interference of transient disturbances, conned transmission systems such as employ `nire circuits are nevertheless auch disturbances may arise in yviresystems from external sources, such as lightning tir-foreign electric systems, or may arise hom sources within the wire system itself as from alter the transmission WBJVQS gifgtlvecn., the said tuned detecting circuit and nations in the energy transmitted. In the case of power suppl circuits, these alternations may be cause by sudden changes of switching, circuit-breaker operation, etc., While in signaling circuits they may be even those characteristic of the signaling itself. Manifestly the method and means described herein are applicable to the rotection of Wire systems against such disturbances.

l/Vhat is claimed is:

1. In a radio signaling system, the combi nation With a detecting circuit tuned to a particular frequency orband of frequencies, of a filter structure functioning not only as a filter but also as a collector of radiant energy, the said structure having series impedance elements and shunt impedance elements proportioned to readily transmit a selected frequency or band of frequencies.

2. In a radio signaling system, the combination with a detecting circuit tuned to particular frequency or band of frequencies, of a filter structure functioning not only as a filter but also as a collector of radiant eri-- ergy, the said structure comprising a plu rality of similar recurrent electrical networks arranged to readily transmit a selected fre quency or band of frequencies, and a uni" directional translating device connected bem the said filter structure. Y n

3. In a radio signaling system, the combi nation `with a filter structure functioning not only as a filter but also as a collector of radiV ant energy, the said structure being tuned to respond to a plurality of frequencies by means of series impedances and shunt impedancesto ground, of a' sharply tuned receivn ing circuit and a unidirectional translating device inserted between the said filter structure and the said receiving circuit.

d. In a radio signaling system, the com? bination with a filter structure functioning not only as a dlter but else as a cullector of radiant energy, the said structure ccmpris ing a plurality of sections tuned to respund to a plurality of frequencies, of a receiving circuit sharply tuned te e. frequency er te a band of: frequencies.

5. lln a radin signaling system, the com@ bination with a lter structure fimetiening net only as a filter but also as a collector cf radiant ener the said, structure comprising a plurality o sections tuned te respondtu a plurality of frequencies, of a sharply tuned receiving circuit, and a unidirectienal tranrun lating device connected between'the said structure and the said resetting circuit.

lin testimony whereof, ll have signed name te this rnieeideatlcn sth day el 'December ldt.

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